1. Technical Field
The present invention relates to a pump arrangement primarily, though not exclusively, for use in vehicles. The invention further relates to a fuel delivery system incorporating such a pump arrangement. The invention also relates to a liquid cooling system for an internal combustion engine incorporating such a pump arrangement.
2. Background Information
In a commercial vehicle fuel delivery system it is known to use a rotary displacement pump driven by the transmission of the vehicle to increase the fuel pressure in the system to a level suitable for injection of the fuel into the vehicle engine. The pump has to be capable of delivering fuel at a sufficient pressure substantially immediately upon starting the engine. This implies that at high engine speeds the pressure in the fuel delivery system is greater than actually required. Consequently, an overpressure valve is required downstream of the pump to relieve the excess pressure.
A conventional rotary displacement pump comprises a housing, a pumping chamber within the housing, pressure increasing means in the form of intermeshing gears within the pumping chamber, and an input shaft to the housing for causing rotation of the intermeshing gears. To prevent leakage of the liquid pumped from the pumping chamber, an adequate sealing means is provided between the housing and the input shaft. Due to the rotation of the input shaft, a dynamic seal must be employed. In the fuel delivery system described above, failure of the sealing means not only implies that fuel leaks out of the system, but also that the leaking fuel may migrate into the transmission, mixing with the lubricant therein. Furthermore, the use of a transmission-driven fuel pump implies that a suitable location for the drive shaft to the pump has to be provided, as well as ensuring correct gearing for the drive shaft. Given the space constraints in modern vehicles, these demands are not always simple to accomplish.
It is also known to use an electrically driven pump for supplying fuel to an internal combustion engine. However, such a pump is not particularly efficient since electrical energy for driving the pump must be generated by the internal combustion engine and thereafter reconverted to mechanical energy in the pump, implying losses during conversion.
Virtually without exception, internal combustion engines used in commercial vehicles require liquid cooling using a coolant. The coolant is pumped through the engine by a water pump. Typically, the water pump is attached to the cylinder block and is driven by a belt from the crankshaft of the engine.
A dual pump system as described in U.S. Pat. No. 3,370,540 is comprised of a first gear pump having a drive member and a driven member, and a second gear pump magnetically driven by the first gear pump. The drive and driven members are made from magnetic material. The second gear pump has an internal gear element with magnetic material peripherally carried thereon juxtaposition to both the drive member and the driven member. The internal gear element is separated from the drive and driven members by an impermeable member attached to the pump body of the first gear pump. Rotation of the drive and driven members allows responsive rotation of the internal gear element. In this manner, two separate liquids may be pumped by the dual pump system. A disadvantage with this dual pump system is that two pump bodies are required, one for the first gear pump and one for the second gear pump.
Another dual pump arrangement is disclosed in DE-A-44 34 244. In that document, two axially arranged pumps are mechanically driven by a common drive shaft, with one pump acting as a fuel pump and the other serving as a power steering pump. A conceivable problem with this arrangement is the risk of leakage of liquid from one pump to the other due to failure of the seals around the common drive shaft.
It is an object of the present invention to provide a pump arrangement suitable for use in commercial vehicles for pumping fuel and coolant, wherein the pump arrangement is potentially more compact, energy efficient and easier to seal than previous arrangements.
This object is achieved in accordance with the present invention by a pump arrangement having a housing, a first pumping chamber within that housing, the first pumping chamber being adapted to be connected to a first liquid transport circuit, a drive shaft carried by the housing, a first pumping means arranged for rotation within said first pumping chamber, the first pumping means being driven by the drive shaft, a second pumping chamber separated from the first pumping chamber by the housing such that the housing forms a common separation wall, the second pumping chamber being adapted to be connected to a second liquid transport circuit, the second pumping chamber accommodating the second pumping means being driven by the drive shaft, wherein the second pumping means is driven by the drive shaft via a magnetic coupling, the coupling comprising a driver rotor connected to the drive shaft and a driven rotor carried by the housing, the driven rotor driving the second pumping means, the driver rotor and the driven rotor being separated by a separation wall assembly serving as a static seal to hermetically seal the second pumping chamber from the drive shaft.
Accordingly, the pump arrangement of the present invention is a single compact unit which is able to pump two separate liquids in respective liquid transport circuits with greatly reduced risk of inadvertent mixing of the two liquids. Furthermore, since the magnetic coupling is only capable of transmitting a predetermined value of torque, the pressure downstream of the pump cannot exceed a predetermined value, irrespective of the rotational speed and/or torque of the input shaft.
The invention further provides for a fuel delivery system incorporating the pump arrangement of the present invention, as well as a liquid cooling system incorporating said pump arrangement.
In addition, the invention provides for a vehicle comprising the fuel delivery system and the liquid cooling system of the present invention.
Further preferred embodiments of the invention are detailed in the dependent claims.